Superplasticity in a coarse-grained as-cast magnesium alloy

Abstract

Superplasticity of a coarse-grained cast Mg–2.5Gd–0.5Zr alloy was investigated by assessing the strain rate sensitivity index (m-value) through the shear punch testing (SPT) method in the temperature range of 623–748 K and shear strain rate range of 2.8 × 10−3–2.2 × 10−2 s−1. The initial as-cast grain size of about 150 μm was reduced to about 3.5 μm at the end of the test. This severe grain refinement caused by dynamic recrystallization (DRX) facilitated superplasticity in the studied cast alloy. According to the respective m-values of 0.51 and 0.53 obtained at 698 and 723 K, and the activation energy of 80 kJ mol−1, the prevailing mechanism of deformation was suggested as grain boundary sliding (GBS) controlled by grain boundary diffusion.